src: split CryptoPemCallback into two functions

Currently the function CryptoPemCallback is used for two things:
1. As a passphrase callback.
2. To avoid the default OpenSSL passphrase routine.

The default OpenSSL passphase routine would apply if both
the callback and the passphrase are null pointers and the typical
behaviour is to prompt for the passphase which is not appropriate in
node.

This commit suggests that the PasswordCallback function only handle
passphrases, and that an additional function named NoPasswordCallback
used for the second case to avoid OpenSSL's passphase routine.

PR-URL: https://github.com/nodejs/node/pull/12827


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>